C#/Unity Camera Follow Jitter due to Time.deltaTime

问题

Game: In a simple 2D Portrait Game made in Unity, I have a GameObject (Player) that has a fixed location and which is moving upwards. The Camera follows the Player and animated Obstacles are spawning from time to time moving left to right. The attached Screenshot shows the Scene.

The Problem: The Movement is not smooth, as it seems like the Player is jittering. I think I already identified one of the causes: Big variation of Time.deltaTime. Average value is 0.0167, but I had variations. Minimum was 0.00177, maximum value was 0.2249519.

Settings: Target Framerate is 60. I use Unity 2019.4.2f1 and as build target an iPhone X with iOS 14.2.

Scripts

public class Player: MonoBehaviour 
{ 
    float speed = 5f; 
    void Update() 
    { 
        transform.Translate(0,speed*Time.deltaTime,0); 
    } 
} 

public class CamFollow : MonoBehaviour 
{ 
    public Transform Player; 
    private Vector3 FollowVector; 
    void LateUpdate() 
    { 
        FollowVector = Player.position - new Vector3(0, -4.0f, 10); 
        transform.position = Vector3.Lerp(transform.position, FollowVector, Time.deltaTime * 4f); 
    } 
}

Note: I need to use Lerp, because the Player may lower or increase the speed for one second, then the camera gently moves to the new position, before changing back. For the Obstacles I don't have a Script. They are moving, by using the Animation Component. For the Obstacles I only loop a change of the x value of the position.

My alternative solutions:

1. Changing the value for Time.deltaTime to a constant value of 0.01666667f:

void Update() 
{ 
    transform.Translate(0,speed*0.01666667f,0); 
}

This makes the Player Object jitter a lot in the Unity Editor but only a little on the device

2. Using Fixed Update both for the Camera Follow and the Player Movement

This makes the movement and camera follow perfectly smooth, but the animated objects jitter a lot. I know Unity wants to adress the deltaTime issue in one of the next updates. But there should be a solution for my problem, so did anybody have a similiar problem, which could be solved? I prefer the 2nd alternative, because the movement looked really smooth and nice, so can I somehow make the animation part of "fixedUpdate"?

回答1:

The variation in the 'deltaTime' is to be expected.

The variation is large on the PC because you are running on a complex computer with a complex operating system and lots of other applications running simultaneously, each with a multitude of threads, which every once in a while want to do some work. Thus, the scheduler of the operating system cannot guarantee that you are going to get a time slice at the precise moment that you want it in order to render your next frame.

The variation is smaller on the mobile device because it is a much simpler machine with a lot less going on, so the scheduler is able to give you time slices close to the precise intervals that you are asking.

You are already taking this variation into account when you do

transform.Translate( 0, speed * Time.deltaTime, 0 );

This is a fundamental technique in game development: the frame rate is never constant, so the distance by which you must move an object on each frame depends on the precise amount of time elapsed between this frame and the previous frame.

So, that part is fine.

Your problem lies in

transform.position = Vector3.Lerp( transform.position, FollowVector, Time.deltaTime * 4f );

Here you are passing Time.deltaTime * 4f for parameter t of Vector3.Lerp(). I have no idea what you are trying to accomplish, but the number you need to pass there needs to be a gradual transition between 0 and 1, and instead you are passing a randomly varying number of seconds multiplied by some magic constant 4. This does not look correct.

A couple of options that I can think of:

Always use 0.5 for t so that the camera always rushes to the right position and then slows down as it gets closer to it.
Calculate a separate speed vector for the camera, then move the camera using a translation just as you do for the player.

来源：https://stackoverflow.com/questions/65649239/c-unity-camera-follow-jitter-due-to-time-deltatime

标签

unity3d

camera

smoothing

jitter